Abstract

Precision and accuracy of lead isotope ratios of a volatile lead species (PbEt4) were determined by coupling a capillary GC to a magnetic sector multicollector ICP-MS. PbEt4 was prepared by ethylation of a certified lead isotope solution (NIST SRM 981). Coupling was achieved by a transfer line, which allowed simultaneous introduction of a thallium standard solution to correct for mass discrimination. Seven isotopes (202Hg, 203Tl, 204Pb, 205Tl, 206Pb, 207Pb, 208Pb) were monitored simultaneously with a transient resolution of 50 ms. Pb isotope ratios for the PbEt4 peaks were calculated using transient peak integrals of each isotope signal. Absolute detection limits were 20 (204Pb), 0.7 (206Pb), 1 (207Pb) and 0.3 pg (208Pb). Precision was assessed for five replicate injections of PbEt4 in iso-octane, corresponding to a total amount of 300 pg of Pb. Precision of isotope ratios for 206Pb, 207Pb and 208Pb were better than 0.07% (RSD), with ratios including 204Pb being one order of magnitude worse. Accuracy using mass bias correction via 203Tl/205Tl ranged from 0.18% for 208Pb/206Pb to 0.9% for 208Pb/204Pb.